The invention relates to layered materials such as clay, which are intercalated by a block copolymer(s) and compatibilized in a polyester matrix polymer.
Ever since the seminal work conducted at Toyota Central Research Laboratories, polymer-clay nanocomposites have generated a lot of interest across industry. The utility of inorganic nanoparticles as additives to enhance polymer performance has been well established. Over the last decade or so, there has been an increased interest in academic and industrial sectors towards the use of inorganic nanoparticles as property enhancing additives. The unique physical properties of these nanocomposites have been explored by such varied industrial sectors as the automotive industry, the packaging industry, and plastics manufactures. These properties include improved mechanical properties, such as elastic modulus and tensile strength, thermal properties such as coefficient of linear thermal expansion and heat distortion temperature, barrier properties, such as oxygen and water vapor transmission rate, flammability resistance, ablation performance, solvent uptake, etc. Some of the related prior art is illustrated in U.S. Pat. Nos. 4,739,007; 4,810,734; 4,894,411; 5,102,948; 5,164,440; 5,164,460; 5,248,720; 5,854,326; and 6,034,163.
In general, the physical property enhancements for these nanocomposites are achieved with less than 20 vol. % addition, and usually less than 10 vol. % addition of the inorganic phase, which is typically clay or organically modified clay. Although these enhancements appear to be a general phenomenon related to the nanoscale dispersion of the inorganic phase, the degree of property enhancement is not universal for all polymers. It has been postulated that the property enhancement is very much dependent on the morphology and degree of dispersion of the inorganic phase in the polymeric matrix.
The clays in the polymer-clay nanocomposites are ideally thought to have three structures: (1) clay tactoids wherein the clay particles are in face-to-face aggregation with no organics inserted within the clay lattice; (2) intercalated clay wherein the clay lattice has been expanded to a thermodynamically defined equilibrium spacing due to the insertion of individual polymer chains, yet maintaining a long range order in the lattice; and (3) exfoliated clay wherein singular clay platelets are randomly suspended in the polymer, resulting from extensive penetration of the polymer into the clay lattice and its subsequent delamination. The greatest property enhancements of the polymer-clay nanocomposites are expected with the latter two structures mentioned herein above.
Clays are hydrophilic hence they are not compatible with most organic molecules, specifically the hydrophobic thermoplastic polymers. There has been considerable effort put towards developing materials and methods for dispersing and compatibilizing nanoclays in polymers like polyesters. This is because polyesters are plastics which are used in large volume in fibers, films, food and beverage containers and engineering applications. Some of the polyesters of most commercial interest are poly(ethylene terepthalate) (PET), poly(butylene terepthalate) (PBT), poly(ethylene napthalate) (PEN) and amorphous glycol modified PET (PETG). Preparation techniques for polyester-clay nanocomposites can be divided into two broad categories. One category is called in-situ incorporation or in-situ polymerization where the smectites are treated and added during polymerization. The clays may be added along with the monomers or during the polymerization process. The other category is to melt mix polyesters with treated clays by a compounding process.
The monomers for polyesters are polar. During the polymerization process, the polarity decreases as the molecular weight increases, phase separation of clay and polymer occurs. Hence compatibility between the clays and polymer is important. To enhance the compatibility of the clays, two general routes exist for in-situ clay incorporation. The first is based on a novel technology developed by AMCOL international corporation as disclosed in U.S. Pat. Nos. 5,578,672; and 5,721,306 where clays treated with a polar polymer like poly(vinylpyrrolidone) (PVP) or poly(vinylalcohol) (PVOH) are exfoliated into ethylene glycol, a monomer for PET. This exfoliation of clay is maintained during polymerization process by altering the polymerization conditions. Eastman Chemical (WO 98/29499) used a similar clay modification technique and introduced directly into the charge of a PET melt polymerization with DMT to prepare PET nanocomposites having an improved oxygen barrier. The other route is in-situ incorporation of an organoclay or synthetic clays or sintered clays like fluoromica (JP 8-73710, JP 8-120071). Organoclays are typically prepared using the ion exchange method where an onium ion (JP 3-62846), ammonium salts (JP 7-166036) are used to expand the clay.
In the melt compounding process, the resin is melt mixed with organoclays (WO 93/04118), synthetic clays or clays modified by a technique developed by AMCOL international corporation (vide, for example, U.S. Pat. Nos. 5,552,469; 5,578,672; 5,698,624; 5,804,613; and 5,830,528). U.S. Pat. No. 5,552,469 discusses a technique for dispersing clays in a water soluble polymer like PVP, PVOH which is then dried, and then melt mixed in a thermoplastic resin. U.S. Pat. No. 5,578,672 discusses a process of modifying clays by mixing it with water and polymer with functional groups. This is then dried and mixed with polymer resins. U.S. Pat. No. 5,698,624 discusses use of monomers with benzene ring, hydroxyl group, carboxyl group or low molecular weight polymers to intercalate clays using nonaqueous solvents. This is then later mixed with polymers like polyesters. U.S. Pat. Nos. 5,804,613 and 5,830,528 discuss a similar method of intercalating clays but with different functional monomers in presence of water, prior to mixing the dried clays with the thermoplastics.
In order to further facilitate delamination and prevent reaggregation of the clay particles, these intercalated clays are required to be compatible with the matrix polymer in which they are to be incorporated. This can be achieved through the careful selection and incorporation of compatibilizing or coupling agents, which consist of a portion which bonds to the surface of the clay and another portion which bonds or interacts favorably with the matrix polymer. Compatibility between the matrix polymer and the clay particles ensures a favorable interaction which promotes the dispersion of the intercalated clay in the matrix polymer. Effective compatibilization leads to a homogenous dispersion of the clay particles in the typically hydrophobic matrix polymer and/or an improved percentage of exfoliated or delaminated clay. Typical agents known in the art include general class of materials such as organosilane, organozirconate and organotitanate coupling agents. However, the choice of the compatibilizing agent is very much dependent on the matrix polymer as well as the specific component used to intercalate the clay, since the compatibilizer has to act as a link between the two.
A survey of the art, makes it clear that there is a lack of general guideline for the selection of the intercalating and compatibilizing agents for a specific matrix polymer and clay combination. Even if one can identify these two necessary components through trial and error, they are usually incorporated as two separate entities, usually in the presence of water followed by drying, in a batch process and finally combined at a separate site with the matrix polymer during melt-processing of the nanocomposite. Such a complex process obviously adds to the cost of development and manufacturing of the final product comprising such a nanocomposite. There is a critical need in the art for a comprehensive strategy for the development of better materials and processes to overcome some of the aforementioned drawbacks.
Imaging elements such as photographic elements usually comprise a flexible thermoplastic base on which is coated the imaging material such as the photosensitive material. The thermoplastic base is usually made of polymers derived from the polyester family such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN) and cellulose triacetate (TAC). Films for color and black and white photography, and motion picture print film are examples of imaging media comprising such flexible plastic bases in roll form. TAC has attributes of high transparency and curl resistance after processing but poor mechanical strength. PET on the other hand has excellent mechanical strength and manufacturability but undesirable post process curl. The two former attributes make PET more amenable to film thinning, enabling the ability to have more frames for the same length of film. Thinning of the film however causes loss in mechanical strength. The stiffness will drop as the cube root of the thickness of the film. Also a photosensitive material coated on the base in a hydrophilic gelatin vehicle will shrink and curl towards the emulsion when dry. There is hence a need for a base that is thinner yet stiff enough to resist this stress due contraction forces. Further, in motion picture print film image distortion arises from thermal buckle of the plastic film caused by the heat generated by the projector bulb. Hence a transparent film base that has dimensional stability at high temperatures due to its higher heat capacity is also highly desirable.
It is an object of the invention to provide an intercalated clay. In some cases, this intercalation might result in exfoliation too. It is a further object of the invention to provide an intercalated clay which further comprises a component compatible with a matrix polymer in which the clay can be dispersed. It is a further object of the invention that the matrix polymer is a polyester resin. It is an even further object of the invention to provide an article comprising a matrix polymer and an intercalated clay wherein said intercalated clay comprises a matrix compatible component. These and other objects of the invention are accomplished by providing an article comprising a matrix polymer and clay wherein said clay is intercalated with a block copolymer, wherein said block copolymer comprises a hydrophilic block capable of intercalating said clay and a matrix compatible block compatible with said matrix polymer.